Coronary heart disease (CHD), which causes heart attacks and angina, is the single leading cause of death in the United States. The strongest risk factors for CHD development include circulating levels of lipids and lipoproteins, both of which are strongly regulated by genetic factors. Variants with significant effects on lipid levels have been identified for a number of monogenic familial disorders, but these account for only a small proportion of CHD. In contrast, genetic determinants for common lipid abnormalities remain unknown. The overall plan for this project is to identify and characterize genetic variants that contribute to the regulation of fasting serum concentrations of total cholesterol. The focus of this study is a locus which has been initially mapped on the basis of linkage data to chromosome 19 in at least 15 studies, then subsequently narrowed to a 1-LOD support interval <15.7 cM in Pima Indians. The specific goals of this proposal are to first refine and prioritize localization of the QTL(s) for fasting serum TC concentration on 19p by genotyping a dense set of SNP markers in a study sample of 2,884 Pima Indians. All QTL-associated SNP alleles and haplotypes will then be genotyped in 701 African American individuals from the Genetics of NIDDM (GENNID) study, in whom we have previously observed linkage for TC concentration, and 740 Mexican American individuals from the San Antonio Family Gallbladder Disease Study (SAFGS), who are more likely to share greater genetic similarity with Pima Indians. Completion of this aim will provide validation of findings obtained in Aim 1. The next step will utilize an innovative bar-code approach to next-generation sequencing to fully characterize regions showing association with TC concentration, and identify specific variants that are likely to exert functional effects on cholesterol metabolism. Finally, we propose an exploratory characterization of functional effects associated with strong QTL-related alleles, which will provide a basis for the development of a full-scale investigation of the molecular mechanisms by which these specific variants affect regulation of cholesterol metabolism as the focus of an independent grant application. Combined, these aims will identify novel variants with critical effects on fasting total cholesterol concentration. Identification of the genetic mechanisms influencing cholesterol concentrations will advance our understanding of lipid metabolism, leading to an enhanced knowledge of the pathophysiology of the atherosclerotic process.